The present invention relates to a sector servo-controlled disk drive, and more specifically to such a disk drive having a servo protection feature.
In a sector servo-controlled disk drive, the position of a read-write head is controlled so that it traces the right track in response to the tracking information recorded in each servocontrol field of the disk driven by a spindle motor. Servo protection is provided to prevent the tracking information from being inadvertently erased. In the current practice, a servo protect pulse is generated in response to an index pulse which is generated for each revolution of the disk to designate the areas that belong to the servocontrol field. Synchronism can be reestablished between the disk and the servo protect pulse only once for each disk rotation. However, a speed variation of the spindle motor causes the servo protect pulse to go out of sync with the disk. To overcome this problem, it has been necessary to provide a sufficient safety margin at each end of the servocontrol field.